1. Area of the Invention
This invention relates to phased array antenna and more particularly relates to a phased array antenna having M+N phase shifters for an M by N antenna array.
2. Description of the Prior Art
Conventional phased array antennas are commonly used in conventional systems where the transmitter, a target for radar, or the receiver, is mobile. By altering the relative phasing of a group of radiating or receiving elements with respect to each other, the beam produced by the overall antenna or the gain pattern of a receiving antenna may be altered or steered.
Typical phased array antennae require complicated three dimensional structures. In the typical antenna array of M by N elements, M and N being integers with at least one of M and N being greater than one, there is a requirement of M times N phase shifters to steer the antenna beam. For an array of ten by ten elements, one hundred phase shifters are required, contributing greatly to the complexity and overall cost of the system.
In addition, incorporating such phase arrayed antennas in patch antennas such as may be used in an aircraft or a vehicle engenders several difficulties. Distribution of the phase array signals from the M times N phase shifters to M times N antenna elements within the array often results in a complicated three dimensional feed structure. Each feed line from the M times N phase shifters will be routed to a different one of the antenna elements and may have to cross several of the feed lines for other elements. Since each line must be insulated from the other lines where they cross, that results in a complex, multilayer structure. Further, the lines must be carefully routed so that the signal on one feed line is not cross coupled to another feed line, causing harmful interference. In addition, the large number of lines that must be routed near each other can also cause problems with impedance matching, requiring an even more complex structure with multiple layers and apertures or feedthroughs between different layers.
If multiple layers are used, the multiple layers also result in a thicker structure. This may cause problems with implementing patch antennas on streamlined surfaces such as airliners.
Therefore, it is a first object of the invention to provide an essentially planar phased array antenna structure to permit a streamlined patch antenna. It is a second object of the invention to provide a simplified feed structure. It is a third object of the invention to provide such a feed structure with fewer phase shifters for controlling the antenna elements within the array. It is yet another object of the invention to provide a phased array antenna that is inexpensive to fabricate.